Machines of this sort are known to feature a supporting frame to which is fitted in a fixed position an injection station for receiving a first half-mold which is locked on to the injection station. The frame also supports a movable frame for supporting a second half-mold, and which is connected to the ends of a number of push rods for keeping the second half-mold perfectly parallel to the first half-mold, and for imparting to the second half-mold a relatively precise approach movement to couple and keep the two half-molds coupled along the whole of their respective peripheries at the injection station.
Known machines of the above type have several drawbacks, mainly due to the presence of the push rods, which prevent free access to the mold, thus complicating maintenance and replacements; transmit externally, i.e. on to the frame, both the forces applied to the half-molds and the forces generated inside the mold, so that relatively strong, high-cost frames must be used; and call for an extremely high degree of assembly and operating precision.